In sport, particularly athletics, international competition is the ultimate challenge to the various regulatory systems of the body: physiological; biochemical; biomechanical and psychological. The body experiences a great challenge to accommodate the metabolic, thermal and other demands of intense exercise, where this challenge is greatest during endurance events in hot environments.
Since water serves the role of controlling most of the body's regulatory systems, the need for fluid intake during exercise is one of the main concerns, if not the primary concern, for the sportsperson in ensuring they can maintain their maximum sporting potential. The body's management of its hydration status is essential in its main roles of regulating body temperature; blood circulation, volume, viscosity and pressure; facilitating muscle movement and for removing waste.
A deficient level of hydration can lead to dehydration, a process referring to a loss of body water, from a state of hyperhydration (greater than normal body water content) to euhydration (normal body water content) or from euhydration downward to hypohydration (less than normal body water content).
In terms of performance, a subject who is just 2% dehydrated can see their performance drop by 20-30%, when compared to being in a state of euhydration. Put in context, this reduction in performance compares to the margin between winning gold and finishing outside of the medals, 7 seconds adrift, in the 1500 m in the 2000 Sydney Olympics.
It is important, however, to emphasise that hydration is not the only factor that should be monitored in exercise. Other factors such as energy stores, levels of electrolytes, fatigue, psychological factors and fitness (reduced fitness in elite athletes is due to insufficient recovery time to regain fitness after sustaining an injury) all have an effect on the performance of the sportsperson, and since the nature of sport is based around precision, an imbalance of any of these factors can lead to underachievement. In extreme cases, it has been known for a deficiency of electrolytes to be fatal, inducing a condition known as hyponatremia. The condition is often brought on through the dilution of sodium content in the blood, where the subject has consumed too much fluid without an adequate replacement of sodium.
It is the occasion where an athlete has the perfect balance of the above factors that they will perform at their lifetime best. A performance such as this requires the mind of the athlete to be in harmony with their body, an occurrence known simply as ‘the zone’. It is an altered state of consciousness where the body and mind function automatically.
It is therefore desirable to be able to monitor hydration levels to achieve maximum possible performance. It is particularly desirable to be able to measure hydration levels during exercise to determine the quantity of liquid that should be taken on board to maintain, or reach, ideal hydration levels.
Current systems used for measuring hydration include osmometers and refractometers. Such systems are used by sporting bodies and clubs, although due to the size of the apparatus involved and the nature of the measurements taken, the systems can only be used before, during a stationary phase, or after an exercise is finished.
Osmometers work on the principle of either freezing point depression or vapour pressure (heating and cooling). Osmometers determine the number of water particles in a blood solution obtained from a subject by taking a blood sample. Another form of osmometry measures the concentration of water in a urine sample. In both cases, osmometry is not practical for use during exercise due to the need to collect blood or urine samples.
Refractometers measure the specific gravity of urine samples. By placing a drop of urine on the screen, the concentration of the urine is read off from a scale, the reading being determined by the refraction of light through the urine. The reading on the scale can then be converted into a number of milli-osmos per Kilogram.
Again, it is not practical for use during exercise due to the need of a urine sample. Although portable skin hydration monitors exist, such devices are designed for use in dermatology as a measure for skin moisture. Skin hydration monitors measure moisture levels in the corneocytes (dead skin cells) in the stratum corneum, the outer layers of the skin. In terms of body water, a normal moisture level in the stratum corneum could either be the result of, firstly, body euhydration or, secondly, sweating whilst in a dehydrated state. It therefore follows that skin hydration levels do not reflect body hydration. It is also not possible to determine the level and quantity of sweat, since the water in the stratum corneum reaches a maximum when the body is in a state of euhydration. Therefore it would not be possible to determine any excess sweat that evaporates or drips off the skin.
It has been suggested that blood flow monitors could be adapted to determine fluid status, through monitoring how peripheral blood flow varies during exercise to facilitate the dissipation of heat by the process of sweat and heat exchange. However, it is thought that this would not be a reliable method of monitoring hydration because sweat rates, and therefore blood flow rates, are greater in hot than in cold climates, even for the same level of dehydration. Peripheral blood flow fails to allow for other means of loosing fluid such as increased fluid exchange in cold climates between the environment and breath, where the environment draws moisture from the breath to try and equalize the two moisture levels.
It is understood from medical studies that for every 1% loss in body weight, due to dehydration, heart rates increase by about 7 beats per minute. From this, it may be possible to develop a heart rate monitor to calculate loss in hydration due to an increase in heart rate. However, it is not thought that such a monitor would be particularly accurate as heart rate increases could also be the result of other factors. For example, an increase in speed from one stride to the next would cause an increase in heart rate, as would anxiety, hormone levels, caffeine intake and the (varying) temperature of the atmosphere.
Bio-electrical Impedance Analysis (BIA) is another technique that has been suggested for use in measuring hydration. BIA analyses the amounts of fat, muscle and water in the body. The measure of hydration is separated into intracellular and extra cellular fluid compartments. BIA works by sending a small current through electrodes attached to the skin, normally on the hand and the foot. The current is sent at two different levels, one that can penetrate the cells of the body and one that cannot. The difference between the two provides an indication of the hydration status, on the theory that fluid facilitates the conduction of current. Currently, BIA results are affected by numerous variables including body position; hydration status; consumption of food and beverages; ambient air and skin temperature; recent physical activity; and the conductance of anything in contact with the skin, other than the electrodes. Thus, BIA lacks the precision and accuracy necessary for hydration monitoring, and it is doubtful that it could ever be adapted for use to determine fluid levels during even gentle exercise.
The present invention seeks to provide means for monitoring hydration in the body during exercise. It was therefore important to understand whether or not the theories behind any existing products could be developed for use in the PHM.